As you can see, the ramdisk solution is the worst of all
in terms of RAM memory footprint;
also it takes a pretty long time to boot.
However, it is one of the few solutions that allow an in-situ
update while the system is running.

JFFS2 is easy to use as it's a writable file system
but it takes a long time to boot.

A read-only ext2 file system shines when boot time and RAM memory
footprint are important; you pay for this with an increased flash memory
footprint.

External flash memory devices like CompactFlash cards or USB memory
sticks can be cheap and efficient solutions especially when
lots of data need to be stored or when easy update procedures are required.